Permonosulfuric acid for bleaching synthetic polymer textiles



United States Patent PERMONOSULFURIC ACID FOR BLEACHING SYNTHETIC POLYMER TEXTILES Eric T. Fell, Ambergate, England, assignor to Stevensons (Dyers) Limited, Amber-gate, England, a corporation of Great Britain No Drawing. Application December 7, 1954 Serial No. 473,737

6 Claims. (Cl. 8-111) This invention relates to the bleaching of nylon and other wholly synthetic linear organic polymer textiles.

Nylon is a synthetic linear polyamide textile fiber, "such as polyhexamethylene adipamide and falls under the designation of synthetic linear organic polymer textiles. Other fibers and fabrics falling under this last-named designation include Orlon which is a linear polyacrylonitrile textile, and other polymers having similar constitutions. The expression thus also includes Perlon and polymerized caprolactam which is a linear polyamide with a shorter carbon chain than nylon.

It is known that bleaching materials suitable for cotton and woolen textiles are generally unsuitable for nylon and the other polymer synthetic textiles mentioned. Thus, the usual bleaching compounds, such as sodium peroxide, sodium perborate, and sodium and calcium hypochlorite and hydrogen peroxide, are injurious to nylon and the other polymer synthetic textiles mentioned. Fabrics and yarns of nylon and the other synthetic linear polymers mentioned usually have a noticeable yellowish grey color which is sometimes exaggerated by preboarding and heat-setting treatments, and it is desirable to remove this color and also other impurities such as oils and sizes which are present due to the spinning or weaving of the textiles mentioned. The problem of bleaching nylon and the other polymers mentioned has existed in the textile industry from the earliest introduction of the several polymer textiles mentioned and has remained unsolved up to the time of the present invention, so far as I am aware.

The principal object of this invention, accordingly, is to provide a simple and efiicient process for bleaching synthetic linear organic polymer textiles and to provide a bleached product having the desired whiteness while retaining substantially all of its other desirable properties.

The invention accordingly consists of the novel products as well as the novel processes and steps of processes according to which such products are manufactured, the specific embodiments of which are described hereinafter by way of example and in accordance with which I now prefer to practice the invention.

I have found, in accordance with my invention, that the bleaching of synthetic linear organic polymer textiles, including those mentioned above, may be accomplished by treating such textile with an acid aqueous bath containing'permonosulphuric acid for a sufiicient time to bleach said textile. In carrying out the process I usually employ a bath which contains an added acid material such as sulphuric acid. The solution, as noted, is an acidic solution and for practical purposes the pH is usually at about 2.5 or less. The temperature may vary over a wide range, from below room temperature to the boiling point of the aqueous bath or above. I generally prefer to employ temperatures between approximately room temperature and the boiling temperature of the bath. The of treatment will vary according to the temperature arid gia'ccording to the strength of the acid bath, that is the amount of permonosulphuric acid employed. Thus,

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the time may range up to 14 hours for dilute solutions of permonosulphuric acid at room temperatures, whereas with stronger solutions the time may run as low as 30 seconds or less. At temperatures of C. up to the boiling point I have found that a practical time of operation is from 15 to 20 minutes.

The following are examples in accordance with the invention as I now prefer to practice it. It is to be understood that these examples are illustrative and that the invention is not to be considered restricted thereto except as indicated in the appended claims.

Example 1.Scoured nylon fabric which has been given the usual heat-set, from which, accordingly, oily matters have been removed but which still has a yellowish grey color, is immersed for fourteen hours at about 20 C. in an aqueous bath containing 7 grams per liter of permonosulphuric acid brought to pH 0.6 by means of sulphuric acid (1.1 grams per liter) and 1.1 grams per liter hydrogen peroxide. After such immersion the fabric is rinsed with cold water and dried. A nylon fabric is thus produced which has the desired whitened effect due to bleaching by the bath while its hand, tensile strength, resistance to abrasion and similar desirable characteristics remain unimpaired.

Example 2.Scoured nylon yarn from which, accordingly, oily matters have been removed but which still has a yellowish grey color, is passed through an aqueous bath at 28 C. containing 5 parts of permonosulphuric acid in parts of water and which contains .8 part of sulphuric acid and .8 part of hydrogen peroxide. The bath has a pH of 0.8. The contact time for the yarn in the bath is approximately 30 seconds. Thereafter the yarn is squeezed so as to express excess treating liquor and then is well rinsed with cold Water and dried. The resulting yarn is whitened while its hand, tensile strength, resistance to abrasion and similar desirable characteristics remain unimpaired.

Example 3. Scoured Perlon fabric which has been given the usual heat-set, from which, accordingly, oily matters have been removed but which still have a yellowish grey color, is immersed in a bath containing one part of permonosulphuric acid in 1000 parts of water and having .2 part of sulphuric acid and .2 part of hydrogen peroxide, producing a pH of 2. The duration of treatment is for one hour with the temperature maintained at approximately 40 C. Excess liquid is pressed out and the fabric is then rinsed with cold water and dried. The fabric has the desired whitened efiect due to bleaching by the bath while its hand, tensile strength, resistance to abrasion and similar desirable characteristics remain unimpaired.

Example 4.Undyed, preboarded, scoured socks made from continuous filament nylon yarn and accordingly having oily matters removed but which still have a yellowish grey color, were entered into a bath containing one pound of permonosulphuric acid with 2.5 ounces of sulphuric acid and 2.5 ounces of hydrogen peroxide in 200 gallons of water at room temperature and at pH 2.3. The bath was quickly brought to 80 C. and thereafter the treatment was continued for 20 minutes. The socks were then pressed to remove excess treating solution, rinsed with cold water and dried. After postboard-f ing by the usual method the socks thus produced were whitened while their hand, tensile strength, resistance to abrasion and similar desirable characteristics remained unimpaired.

The above Examples 1 to 4 were repeated under exactly the same conditions as'therein given with the exception that hydrogen peroxide was omitted. The results were the same as given at the ends of said examples.

Example 5.Undyed, preboarded, mens socks made from Orlon, from which, accordingly, oily matters have been removed but which still have a yellowish grey color,

are boiled in an aqueous solution containing 4 grams" per liter of permonosulphuric acid containing 0.6 gram per liter of sulphuric acid. The solution has a pH of 1.2. The treatment is for 20 minutes. The socks are then squeezed and well rinsed with cold water and postboarded by the normal method. The socks thus produced have the desired whitened effect due to bleaching by the bath while their hand, tensile strength, resistance to abrasion and similar desirable characteristics remain unimpaired.

Example 6.-Undyed, preboarded ladies stockings made from nylon yarn from which, accordingly, oily abrasion and similar desirable characteristics remain unimpaired.

The above Examples 5 and 6, inclusive, were repeated under exactly the same conditions as given in each example but with the presence of the following amounts of hydrogen peroxide:

Example: Gr./liter hydrogen peroxide 5 0.6 6 0.1

The results, employing the examples thus including hydrogen peroxide, were substantially the same as those given at the end of each of the examples mentioned.

Where solutions are employed at the boil I have found it more desirable to omit hydrogen peroxide and these solutions were accordingly made as indicated below with the use of salts of permonosulphuric acid combined with sulphuric acid. The solutions, with or without hydrogen peroxide, operate to effect the bleach in substantially the same manner. However, the solutions containing hydrogen peroxide tend slowly to decompose at boiling temperatures and the consequence is that they must be replenished with permonosulphuric acid from time to time. In addition, we have found that it is important to employ solutions containing not over 1.5% of permonosulphuric acid without hydrogen peroxide when the solutions are employed at the boil since solutions above this content appear to decompose more readily and require replenishment of permonosulphuric acid.

. The solutions of permonosulphuric acid with sulphuric acid may be prepared by known processes employing potassium persulphate or similar persulphate and sulphuric acid in aqueous solution. The solutions so prepared are all acidic solutions, that is having a pH less than pH 7 and preferably containing a range of .5 to 15 grams per liter of the aqueous solution of permonosulphuric acid and .1 to 3 grams per liter of the aqueous solution of sulphuric acid. Solutions containing permonosulphuric acid and sulphuric acid may also be prepared in accordance with my copending application Ser. No. 398,195, filed December 14, 1953, and now US. Patent No. 2,789,954, in accordance with which regulated amounts of concentrated sulphuric acid of not less than about 88 B. and hydrogen peroxide are flowed together to produce permonosulphuric acid, sulphuric acid, water and hydrogen peroxide having a content of over 15% permonosulphuric acid. The resulting mixture is then cooled as it flows to inhibit substantially further reaction and the flowing mixture is diluted with water to produce a solution containing not more than 15% permonosulphuric acid. The resulting composition is stable and contains an appreciable amount to about 15 of permonosulphuric acid, an appreciable amount to about 5% of hydrogen peroxide, and an appreciable amount to about 15 of sulphuric acid and the balance water, all parts being'by weight. The composition in the ranges mentioned may be employed by me for the bleaching of nylon to give a nylon yarn or fabric having the characteristics mentioned in the examples above.

What I claim is:

l. A process which comprises, contacting a wholly synthetic linear organic polymer textile selected from the group consisting of a polyamide textile and a polyacrylonitrile textile with an acid aqueous bath containing permonosulphuric acid for a sufficient time to bleach said textile, while preserving its desirable characteristics unimpaired.

2. A process which comprises, contacting a synthetic linear organic polymer textile selected from the group consisting of a polyamide textile and a polyacrlyonitrile textile with an acid aqueous bath containing permonosulphuric acid and. sulphuric acid at a pH of not over about 2.5 for a sufiicient time to bleach said textile, while preserving its desirable characteristics unimpaired.

3. A process which comprises, contacting a linear polyamide textile with an acid aqueous solution containing permonosulphuric acid and sulphuric acid for a sufficient time to bleach said textile, while preserving its desirable characteristics unimpaired.

4. A process which comprises, contacting a linear polyacrylonitrile textile with an acid aqueous solution containing permonosulphuric acid and sulphuric acid for a sufficient time to bleach said textile, while preserving its desirable characteristics unimpaired.

. 5. A process which comprises, contacting a synthetic linear organic polymer textile selected from the group References Cited in the file of this patent UNITED STATES PATENTS 2,077,103 Franz Apr. 13, 1937 2,426,142 Campbell Aug. 19, 1947 2,432,448 Richards Dec. 9, 1947 2,643,934 Scheiderbauer June 30, 1953 2,701,178 Fell Feb. 1, 1955 2,720,440 Wallace Oct. 11, 1955 2,720,441 Wallace Oct. 11, 1955 2,739,034 Fell Mar. 20,1956

FOREIGN PATENTS I 784,828 France May 6, 1935 798,566 France Mar. 10, 1936 OTHER REFERENCES Easton: Successful Bleaching of Type 670 Nylon, Mod. Tex. Magazine, April 1954, pp. 66 and 68.

Anon.: Am. Dyest. Reptr., Bleaching Dacron Polyester Fiber, Dec. 21, 1953, p. 894. I

Dupont, Customer Service, Nylon, p313.02, March 

1. A PROCESS WHICH COMPRISES, CONTACTING A WHOLLY SYNTHETIC LINEAR ORGANIC POLYMER TEXTILE SELECTED FROM THE GROUP CONSISTING OF A POLYAMIDE TEXTILE AND A POLYACRYLONITRILE TEXTILE WITH AN ACID AQUEOUS BATH CONTAINING PERMONOSULPHURIC ACID FOR A SUFFICIENT TIME TO BLEACH SAID TEXTILE, WHILE PRESERVING ITS DESIRABLE CHARACTERISTICS UNIMPAIRED. 